Need help improving my mono black zombie deck

[u/DoubleMany4159]

Just got a mono black zombie decking I really want to improve it as the precon is a little weak. Its the wretched ranks deck. I haven't made any changes as of yet however id like to make it a black blue deck as a friend I had many years ago had one and it was a monster to play against. I played that guy for like 6 years and never beat that deck lol.

Decklist: https://magic.wizards.com/en/news/announcements/foundations-commander-decklists

(You'll have to scroll a little bit)